Originally Posted by DJ's left nut
Oh, and you're wrong on the engine breaking thing - you don't use more gas when the RPMs come up during engine breaking. The RPMs are only rising due to the compression in the motor and the motor spinning down. It's not actually using any more fuel; it's the transmission turning the motor in the absence of fuel, rather than the motor turning the transmission. The RPMs come up because there's no place for the energy that the transmission is imparting on the motor to go (i.e. the engine compression) so the RPMs spin up and the compression finally peters the acceleration out. If you were actually feeding the motor fuel to create those RPMs, it wouldn't decelerate.
Yeah, this whole "coasting down hills in neutral saves gas" thing is apparently a myth. I used to believe it but I've read too many articles by car guys who knew what they were doing saying that the RPM difference in that situation was deceptive. Most of the insane hypermiler techniques that work don't depend on a manual. There might be a small benefit with idling in neutral at a stop.
I still prefer manuals, they are cheaper and more fun to drive, but most of the gas savings come from efficient shifting, not throwing it in neutral.